1. Field of the Disclosure
The present disclosure relates to a glass composition, and a method for producing the glass composition, having an improved infrared transmission. More particularly, the present disclosure relates to improved infrared transmitting chalcogenide glasses having indium and/or cadmium.
2. Field of the Related Art
A chalcogenide is a chemical compound having at least one chalcogen anion and one more electropositive element. Chalcogens include chemical elements in group 16 of the periodic table, the oxygen family, but excluding oxygen itself. Chalcogenide glasses contain chalcogens, generally sulfides, selenides, and tellurides. Many chalcogenide glasses are sulfur-based with arsenic-sulfur (As—S) or germanium-sulfur (Ge—S) bonds. Applications for chalcogenide glasses typically involve the 8-14 μm wavelength range. It is generally observed that ppm levels of oxygen contamination cause reduced transmission. It is believed that this reduced transmission is due to the absorption of light by germanium-oxygen (Ge—O) or arsenic-oxygen (As—O) bonds that form during the melting process for formation of the glass. This, in turn, leads to reduced performance for optical properties or systems that have this glass.
To improve transmission, glass is often processed by distillation with or without the presence of reactive chemicals, such as Al, Mg, AlCl3 or TeCl4. However, the transmission improvement is usually slight. Also, significant cost increases are associated with the complex processing required by this distillation process. Alternately, the glass can be prepared from exceptionally pure raw materials, however this will add to the cost of the batch. Also, these raw materials can be difficult to source, as well as handle in manner that does not introduce oxygen.
Also, improved IR transmission is important for applications involving thermal imaging, spectroscopy, and CO2 laser transmission, to name a few. In order to achieve sufficient transmission, soft hygroscopic and toxic crystalline materials are often used. However, such materials are also limited in terms of fabrication methods that can be used, namely fiber drawing and lens molding.
FIG. 1 shows the prior art arsenic-selenium (As—Se) glass. In this prior art glass, there occurs arsenic-oxygen (As—O) bonds with absorption near 14 μm. The presence of germanium (Ge) in germanium-arsenic-selenium (Ge—As—Se) glass or germanium-antimony-selenium (Ge—Sb—Se) glass results in germanium-oxygen (Ge—O) bonds and absorption (i.e., a drop in transmittance) near 12.5 μm. The difference in wavelengths for these absorption features, shown in FIG. 1, is due to the frequency of the bond vibration that is a function of bond strength divided by the atomic mass of the atoms. Thus, a metal with lower bond energy and with oxygen or higher atomic mass will result in a lower frequency vibration and longer wavelengths for the absorption.
Thus, there is a need to increase the transmission of typical glass in order to address new applications that are not otherwise suitable for traditional glass or crystals.